Method for preparing polyvinyl butyral by recycling eutectic solvent catalyst mother liquor

Abstract

The invention discloses a method for preparing polyvinyl butyral by recycling eutectic solvent catalyst mother liquor. Specifically, the method comprises the following steps: 1) carrying out an aldolization reaction on polyvinyl alcohol and n-butyraldehyde in a mixed aqueous solution; (2) after the aldolization reaction is finished, carrying out suction filtration and water washing, and carrying out solid-liquid separation to obtain polyvinyl butyral and eutectic solvent catalyst mother liquor; 3) distilling to remove n-butyraldehyde which is not completely reacted in the eutectic solvent catalyst mother liquor to obtain circulating mother liquor; and 4) adding a new raw material into the circulating mother liquor, supplementing a small amount of catalyst and emulsifier, and carrying out the next round of aldolization reaction. According to the invention, the eutectic solvent catalyst mother liquor can be recycled, and residual n-butyraldehyde in the mother liquor can be removed and recovered, so that the next aldolization reaction can be smoothly carried out, the production cost can be reduced, and secondary environmental pollution caused by the fact that catalyst slurry enters wastewater is avoided.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a method for preparing polyvinyl butyral by recycling a low eutectic solvent catalyst mother liquid. Background Art

[0002] Polyvinyl butyral (PVB) resin is white or slightly yellow solid particles or powder, which is formed by the condensation reaction of polyvinyl alcohol (PVA) and n-butyraldehyde. The special functional group structure of PVB resin makes it have excellent coating transparency, elasticity / toughness, insulation, aging resistance, strong alkali resistance, weather resistance, oil resistance and impact resistance at low temperature, etc. It also has good adhesion to glass, metal, ceramics, leather and other materials, making it an indispensable synthetic resin and an ideal material for laminated safety glass.

[0003] Patent CN116041588A reports a method for preparing polyvinyl butyral using a low eutectic solvent catalyzed by a low eutectic solvent (DES) catalyst is prepared by combining tetrabutylammonium bromide and p-toluenesulfonic acid, and sodium polyacrylate (PAA-Na) is used as an emulsifier to efficiently synthesize high-viscosity PVB resin. It can solve the problems of uneven distribution of acetalization degree and low acetalization degree caused by uneven precipitation of PVB in the early stage of the reaction, and can better produce high-quality PVB products. However, when DES is used as a catalyst, it is necessary to add 0.2 equivalents to 5 equivalents of catalyst compared to the mass of the raw material PVA to drive the reaction. The addition amount is very high, and the DES catalyst mother liquor needs to be recycled and reused. If the catalyst mother liquor is directly used after filtration, on the one hand, the catalyst will be partially lost; on the other hand, due to the residual n-butyraldehyde in the mother liquor, the product will react in advance, the obtained PVB product particles are larger, and the acetalization degree decreases, and the initial effect cannot be achieved. Therefore, it is very necessary to explore how to efficiently remove residual n-butyraldehyde in the mother liquor and add appropriate catalysts to efficiently utilize the catalyst mother liquor to synthesize high-viscosity PVB resin. Summary of the invention

[0004] The object of the present invention is to provide a process for recycling a low eutectic solvent catalyst used in an acetalization reaction of polyvinyl alcohol and n-butyraldehyde, so as to solve the problem of catalyst loss and reduce production costs, while also avoiding the catalyst slurry entering wastewater to cause secondary environmental pollution.

[0005] A method for preparing polyvinyl butyral by recycling a deep eutectic solvent catalyst mother solution comprises the following steps:

[0006] (1) adding water to polyvinyl alcohol, stirring at a first temperature until the polyvinyl alcohol is fully dissolved to form a polyvinyl alcohol aqueous solution; dropping an aqueous solution of sodium polyacrylate and a low eutectic solvent catalyst into the polyvinyl alcohol aqueous solution while stirring to form a mixed aqueous solution system; dropping n-butyraldehyde into the mixed aqueous solution system while stirring at a second temperature to cause an acetalization reaction; and maintaining the temperature at a third temperature to make the acetalization reaction more complete.

[0007] (2) After the acetalization reaction is completed, after suction filtration and water washing, solid-liquid separation is performed to obtain polyvinyl butyral and a low eutectic solvent catalyst mother liquid;

[0008] (3) distilling the low eutectic solvent catalyst mother liquor to remove residual low-boiling point n-butyraldehyde to obtain a circulating mother liquor, wherein the residual n-butyraldehyde content in the circulating mother liquor is less than 1 wt % of the amount of n-butyraldehyde added in step (1);

[0009] (4) adding a small amount of sodium polyacrylate and a low eutectic solvent to the circulating mother liquor, and stirring thoroughly to form a first prepared liquid; adding polyvinyl alcohol to the first prepared liquid, and stirring at a first temperature until the polyvinyl alcohol is fully dissolved to form a second prepared liquid; at the second temperature, adding n-butyraldehyde dropwise to the second prepared liquid while stirring to cause an acetalization reaction; keeping the temperature at a third temperature to make the acetalization reaction more complete; after the acetalization reaction is completed, filtering, washing with water, and separating the solid and liquid to obtain polyvinyl alcohol butyral and a low eutectic solvent catalyst mother liquor.

[0010] Furthermore, the low eutectic solvent added in step (4) is 0-30% of the amount of the low eutectic solvent added in step (1); and the sodium polyacrylate added is 10-40% of the amount of the sodium polyacrylate added in step (1).

[0011] Furthermore, the low eutectic solvent added in step (4) is 10-20% of the amount of the low eutectic solvent added in step (1); and the sodium polyacrylate added is 30-40% of the amount of the sodium polyacrylate added in step (1).

[0012] Furthermore, in step (3), the distillation temperature is 75-100° C., and the distillation time is 0.5-2 h.

[0013] Furthermore, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol aqueous solution in step (1) is 1% to 20%, and the mass percentage of polyvinyl alcohol in the second preparation in step (4) is 1% to 20%.

[0014] Furthermore, in the step (1), the mass ratio of sodium polyacrylate to polyvinyl alcohol is (0.001-0.2):1; in the step (4), the mass ratio of sodium polyacrylate to polyvinyl alcohol in the second preparation liquid is (0.0008-0.22):1.

[0015] Furthermore, the low eutectic solvent in step (1) and step (4) is obtained by reacting tetrabutylammonium bromide with p-toluenesulfonic acid monohydrate.

[0016] Furthermore, in the step (1), the mass ratio of the low eutectic solvent to the polyvinyl alcohol is (0.2-5.0):1; in the step (4), the mass ratio of the low eutectic solvent to the polyvinyl alcohol in the second preparation is (0.17-5.75):1.

[0017] Furthermore, in the steps (1) and (4), the mass ratio of n-butyraldehyde to polyvinyl alcohol is (0.5-2.2):1.

[0018] Furthermore, in the step (1) and the step (4), the first temperature is 90°C to 100°C; the second temperature is 3°C to 30°C; the third temperature is 30°C to 60°C, and the insulation time is 1h to 3h.

[0019] The content of n-butyraldehyde in the catalyst mother liquor and the circulating mother liquor of the deep eutectic solvent of the present invention is determined by ultraviolet spectrophotometry. First, different concentrations of n-butyraldehyde are prepared, and the spectrophotometry thereof is measured to make a standard curve, and a linear regression equation is obtained by linear fitting:

[0020] Y=-0.0778+0.8322X (1)

[0021] In formula (1): Y is the volume fraction of n-butyraldehyde, %; X is the spectrophotometer, 1.

[0022] By measuring the spectrophotometry in the mother liquor, the residual n-butyraldehyde content in the corresponding mother liquor can be obtained according to formula (1).

[0023] The present invention has the following beneficial effects:

[0024] The invention recovers the low eutectic solvent catalyst mother liquor and then removes the residual n-butyraldehyde in the mother liquor by distillation, thereby effectively avoiding the premature generation of PVB with large particle size, easy agglomeration and reduced acetalization degree due to the residual n-butyraldehyde in the mother liquor when adding polyvinyl alcohol; after removing the residual n-butyraldehyde, a small amount of DES catalyst and sodium polyacrylate are added, and finally n-butyraldehyde is added dropwise to cause a condensation reaction, thereby obtaining PVB with good morphology, uniform and fine particle size, and no reduction in acetalization degree, which can reach 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the FT-IR spectrum of polyvinyl butyral prepared by recycling the deep eutectic solvent catalyst mother solution in Example 1. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions in this application, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0027] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. The test methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer. Unless otherwise specified, all percentages and parts are by weight.

[0028] In step (1) and step (4), the model of the polyvinyl alcohol (PVA) may include at least one of PVA1799, PVA1797, PVA1795, PVA1788, PVA1999, PVA2099, PVA2488, and PVA2699. In the model of the polyvinyl alcohol, the first two digits represent the degree of polymerization of the polyvinyl alcohol, and the last two digits represent the degree of alcoholysis of vinyl acetate. For example, PVA1799 refers to a polyvinyl alcohol having a degree of polymerization of 1700 and a degree of alcoholysis of 99% of vinyl acetate.

[0029] The sodium polyacrylate can be sodium polyacrylate of different molecular weights. The molar mass of the sodium polyacrylate in the embodiment of the present invention is 4kg / mol to 5kg / mol. The mass ratio of the sodium polyacrylate to the polyvinyl alcohol is (0.001-0.2):1.

[0030] The DES is used as a catalyst and can be obtained by reacting tetrabutylammonium bromide with p-toluenesulfonic acid monohydrate and dissolving in water. In some embodiments, the preparation method of the DES catalyst comprises: weighing 5g to 15g of tetrabutylammonium bromide and 5g to 15g of p-toluenesulfonic acid, adding them to a wide-mouth bottle, putting in a magnet, covering the bottle cap, and sealing it tightly with tape. Then put it in a water bath and stir the reaction at 60°C to 70°C until the solution is clear and transparent (about 2 hours), and the preparation is completed. The addition of a small amount of DES catalyst and PAA-Na emulsifier described in step (4) is mainly because there will be a small amount of loss during filtration and water washing in step (2).

[0031] The technical scheme of the present invention is described in detail below in conjunction with the embodiments. The following embodiments are implemented on the premise of the technical scheme of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Comparative Example 1

[0033] Preparation of deep eutectic solvent (DES) catalyst: Weigh 12.84g of tetrabutylammonium bromide and 11.72g of p-toluenesulfonic acid into a wide-mouth bottle, put in a magnet, cover the bottle cap, and seal it tightly with tape. Then put it in a water bath and stir the reaction at 60℃~70℃ until the solution becomes clear and transparent.

[0034] Weigh 4.6g of PVA in a 250mL three-necked flask, add 57.5mL of water, open the condensed water, stir and heat to 95℃, so that the PVA is fully dissolved to a uniform and transparent state. Then weigh 0.1242g of sodium polyacrylate (molar mass is 4kg / mol~5kg / mol) and 3.22g of DES catalyst, dissolve them in 50mL of water, and add them dropwise to the three-necked flask while stirring. Cool down to 20℃, measure 3.94mL of n-butyraldehyde and add it dropwise to the three-necked flask, and continue to react for 3h. Finally, heat to 45℃ and keep the reaction for 1h.

[0035] After the acetalization reaction is completed, the PVB product and the low eutectic solvent catalyst mother liquor are obtained through suction filtration and water washing.

[0036] The experiment of Comparative Example 1 was repeated 8 times, and 8 portions of deep eutectic solvent catalyst mother solutions were recovered in total. The experiments of Examples 1 to 7 and Comparative Example 2 were carried out using the 8 portions of deep eutectic solvent catalyst mother solutions.

[0037] Examples 1 to 7

[0038] The low eutectic solvent catalyst mother liquor in Comparative Example 1 was recovered. After testing, the residual amount of n-butyraldehyde in the low eutectic solvent catalyst mother liquor was 0.3 mL, accounting for about 7.6% of the total input. Subsequently, the low eutectic solvent catalyst mother liquor was distilled, the temperature was raised to 75-100° C., the distillation time was 0.5-2 h (for example, when the distillation temperature was 90° C., the distillation time was about 1 h), and a small amount of liquid was evaporated to obtain a circulating mother liquor. After testing, the residual amount of n-butyraldehyde in the circulating mother liquor was 0.03 mL, accounting for about 0.8% of the total input.

[0039] The circulating mother liquor was used as a catalyst to carry out a circulation test. A small amount of catalyst and emulsifier was added to the circulating mother liquor, and the mixture was stirred thoroughly to form the first preparation liquid (the addition amounts of catalysts and emulsifiers in Examples 1 to 7 are shown in Table 1); then 4.6 g of PVA was added, the temperature was raised to 95°C, and the PVA was stirred until it was fully dissolved to form the second preparation liquid. The temperature was lowered to 20°C, 3.94 mL of n-butyraldehyde was measured and added dropwise to the second preparation liquid, and the reaction was continued for 3 hours. Finally, the temperature was raised to 45°C and the reaction was kept warm for 1 hour. After the acetal reaction was completed, the PVB product was obtained after filtration and washing.

[0040] Comparative Example 2

[0041] Comparative Example 2 is different from Examples 1 to 7 in that no catalyst and emulsifier are added to the circulating mother liquid, and other circulation test steps are the same as Example 1.

[0042] Table 1

[0043]

[0044] As can be seen from Table 1, in Comparative Example 1, when DES was used to initially catalyze the reaction of polyvinyl alcohol and n-butyraldehyde, the obtained PVB product had an acetalization degree of 83.4%, and the product was fine particles. The recovered low eutectic solvent catalyst mother liquor was distilled to remove residual n-butyraldehyde to obtain a circulating mother liquor. In Comparative Example 2, using the circulating mother liquor, without adding DES catalyst and PAA-Na emulsifier, the acetalization degree of the obtained PVB product decreased significantly, and the product agglomerated. This is due to the incomplete acetalization reaction caused by the partial loss of the catalyst and the agglomeration of the product caused by the loss of PAA-Na. In Examples 1 to 3, when 0.037g of PAA-Na (30% of the initial addition amount) was added, and 0.322g, 0.483g and 0.644g of DES (10%, 15% and 20% of the initial addition amount, respectively) were added for condensation reaction, the acetalization degrees were all above 80%, and the products were all fine particles. When the amount of DES added was 15% and 20%, the acetalization degree was close to that of Experiment 1. In Examples 4 and 5, 15% DES was added, and 0.012g and 0.025g PAA-Na (respectively 10% and 20% of the initial addition amount) were added. The acetalization degree of the obtained PVB was above 78%, but the particle size of the product became larger, agglomeration occurred, and the effect was not the best. Continuing to increase the amount of PAA-Na added (30% to 40%), it is helpful to reduce the particle size of the product, such as Examples 1 to 3 and Examples 6 to 7.

[0045] At the same time, the structure of the PVB resin obtained from the deep eutectic solvent catalyst mother liquid circulation experiment was compared and analyzed using a Fourier transform infrared spectrometer. The infrared spectra of the PVB of Comparative Example 1, Comparative Example 2 and Example 1 are shown in FIG. Figure 1 , their infrared spectra are basically the same. Before testing, the sample needs to be pressed at 120°C. It can be seen that at 1000cm -1 Two groups of vibration peaks of COC structure were obtained around 3000cm -1Two groups of peaks containing -CH3 and -CH2 were obtained, which are consistent with the structure of the standard PVB sample. The infrared spectrum of the experimentally prepared PVB product is basically consistent with that of the standard PVB sample, which shows that the PVB resin product is successfully prepared by catalytic cycle reaction of PVA and n-butyraldehyde in a low eutectic solvent catalyst mother liquid. Although the embodiments of the present invention have been described above, it can be understood that the above embodiments are exemplary and cannot be construed as limitations of the present invention. Ordinary technicians in this field can also change, modify and replace the above embodiments without departing from the concept of the present invention.

Claims

1. A method for preparing polyvinyl butyral by recycling a deep eutectic solvent catalyst mother solution, characterized in that: The following steps are involved: (1) adding water to polyvinyl alcohol, stirring at a first temperature until the polyvinyl alcohol is fully dissolved to form a polyvinyl alcohol aqueous solution; dropping an aqueous solution of sodium polyacrylate and a low eutectic solvent catalyst into the polyvinyl alcohol aqueous solution while stirring to form a mixed aqueous solution system; dropping n-butyraldehyde into the mixed aqueous solution system while stirring at a second temperature to cause an acetalization reaction; and maintaining the temperature at a third temperature to make the acetalization reaction more complete. (2) After the acetalization reaction is completed, after suction filtration and water washing, solid-liquid separation is performed to obtain polyvinyl butyral and a low eutectic solvent catalyst mother liquid; (3) distilling the low eutectic solvent catalyst mother liquor to remove residual low-boiling point n-butyraldehyde to obtain a circulating mother liquor, wherein the residual n-butyraldehyde content in the circulating mother liquor is less than 1 wt % of the amount of n-butyraldehyde added in step (1); (4) adding a small amount of sodium polyacrylate and a low eutectic solvent to the circulating mother liquor, and stirring thoroughly to form a first prepared liquid; adding polyvinyl alcohol to the first prepared liquid, and stirring at a first temperature until the polyvinyl alcohol is fully dissolved to form a second prepared liquid; at the second temperature, adding n-butyraldehyde dropwise to the second prepared liquid while stirring to cause an acetalization reaction; keeping the temperature at a third temperature to make the acetalization reaction more complete; after the acetalization reaction is completed, filtering, washing with water, and separating the solid and liquid to obtain polyvinyl alcohol butyral and a low eutectic solvent catalyst mother liquor.

2. The method according to claim 1, characterized in that: The low eutectic solvent added in step (4) is 0-30% of the amount of the low eutectic solvent added in step (1); the sodium polyacrylate added is 10-40% of the amount of the sodium polyacrylate added in step (1).

3. The method according to claim 2, characterized in that The additional low eutectic solvent in step (4) is 10-20% of the amount of the low eutectic solvent added in step (1); the additional sodium polyacrylate is 30-40% of the amount of the sodium polyacrylate added in step (1).

4. The method according to claim 1, characterized in that: The distillation temperature in step (3) is 75-100° C. and the distillation time is 0.5-2 h.

5. The method according to claim 1, characterized in that The mass percentage of polyvinyl alcohol in the polyvinyl alcohol aqueous solution in step (1) is 1% to 20%, and the mass percentage of polyvinyl alcohol in the second preparation solution in step (4) is 1% to 20%.

6. The method according to claims 1 to 5, characterized in that: In the step (1), the mass ratio of sodium polyacrylate to polyvinyl alcohol is (0.001-0.2):1; in the step (4), the mass ratio of sodium polyacrylate to polyvinyl alcohol in the second preparation solution is (0.0008-0.22):

1.

7. The method according to claims 1 to 5, characterized in that: The low eutectic solvent in step (1) and step (4) is obtained by reacting tetrabutylammonium bromide with p-toluenesulfonic acid monohydrate.

8. The method according to claims 1 to 5, characterized in that: In the step (1), the mass ratio of the low eutectic solvent to the polyvinyl alcohol is (0.2-5.0):1; in the step (4), the mass ratio of the low eutectic solvent to the polyvinyl alcohol in the second preparation is (0.17-5.75):

1.

9. The method according to claims 1 to 5, characterized in that: In the steps (1) and (4), the mass ratio of n-butyraldehyde to polyvinyl alcohol is (0.5-2.2):

1.

10. The method according to claims 1 to 5, characterized in that: In the step (1) and the step (4), the first temperature is 90°C to 100°C; the second temperature is 3°C to 30°C; the third temperature is 30°C to 60°C, and the insulation time is 1h to 3h.

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